1. Field of the Invention
The present invention relates to multi-cell batteries and more particularly to secondary, or rechargeable, multi-cell batteries.
2. State of the Art
In the construction of batteries, typically, individual cells of relatively small current-producing capacity are connected together in parallel to form a multi-cell battery having a larger current capacity. The problem arises in multi-cell batteries that if one of the cells fails, developing an internal short circuit, it also discharges other cells connected in parallel with it, causing the current of all the batteries in parallel to pass through the short circuit. An internal short circuit in a cell will generate heat. If enough current is available to flow through the short circuit, the heat generated can cause the components of the battery to catch fire. A single cell can be designed such that it does not contain sufficient current to cause a fire if an internal short is developed. However, in order to have sufficient current for the battery's intended use, many such cells may be connected in parallel within a battery.
In primary, non-rechargeable batteries, this problem has been addressed by isolating the individual battery cells using diodes. Diodes are placed in series with each battery cell so as to allow current to flow in the discharge direction only, not in the opposite direction (the direction in which current would flow to discharge other parallel-connected cells). Such diode isolation is not applicable to secondary batteries, however, because the diodes would prevent recharging.
What is needed, then, is an arrangement to limit the current to a shorted cell but allow recharging of the entire battery.